Electrical heating iron and method of making the same



Nav. 21, 1939. J, D, Mmm.y 2,180,603

ELECTRICAL HEATING IRQN AND-METHOD 0F MAKING ''HE SAME Filed Nov. 16, 1936 INVENToR JOHN D. MORGAN BY ATroRNEx Patented Nov. 21, 199

UNITED STATES ELECTRICAL HEATING IRON DIETHOD F MAKING THE SAME John D. Morgan, South Orange, N. J., assi-snor to Power Patents Company, Hillside, N. J., a

corporation of Maine Application November 16, 1936. Serial No. 111,092

50laims.

This invention relates to irons land more particularly to electrical heating 'irons and the method of making same, such irons being suitable for ironing and pressing cloth, clothes and the like. A

The electric iron in common use for domestic and household purposes does not require a high temperature heating and accordingly the resistance heating wire is generally enclosed in a good dielectric heating envelope and the heat from the resistance wire is driven through the dielectric material. The heating envelope is usually composed of materials such as mica, asbestos. China clay, magnesium oxide, aluminum oxide and the like. These materials are all fairly good dielectric materials but their thermal conductivity is very low or poor. Accordingly it is necessary to develop very high temperatures in the heating wire in order to force the heat through the usual heat-resisting dielectric materials. Such heating is very inemcient because the dielectrics require a comparatively high temperature differential to get the heat through them and a tremendous amount of heat is wasted in heat transfer energy. This type of iron does not have much heat capacity and cools quite rapidly.

'Ihe irons used for industrial purposes are constructed differently from the household irons and are subjected to much more severe heating conditions in laundries, tailoring shops. In pressing establishments the irons often are heated steadily for ten to fteen hours per day and the temperatures used with such irons are very much higher. Most of these irons are used in conjunction with steam and many of them are required to superheat the steam that is being used. The steam has a very high thermal capacity and tends to rapidly cool the iron. On account of this high heat requirement the heating elements are heated to a very high temperature, that is very much higher than is required for carrying on the work, this high temperature being necsary in vorder to give a suillcient heating capacity. These irons are usually operated thermo- 4;,A statically or they may be provided with a series oi' heating wires that are operated similarly to a rheostat. It is quite common for the heating `elements of the industrial irons to burn out in a comparatively short time and therefore these heating elements are built so as to be easily replaceable.

One object of the present invention is to provide an electrical heating element for an iron that will provide a high heating efficiency for heat transfer with a large heating capacity.

Another object of the invention is to provide a heating element for irons which will give the necessary heating capacity when using a comparatively low temperature heating resistor.

A further object of` the invention is to provide a heating element for an iron which will permit substantially continuous heating service without failure. l A further object of the invention is to provide a method of making irons which is simple and will provide an iron of high quality.

With these and other objects in View the invention consists in the improved electric iron heating element and method of making electric irons hereinafter described and particularly defined in the claims.

The various features of the invention are illustrated in the accompanying drawing in which Fig. 1 is a top plan view with parts in section and parts broken away showing the improved heating element in an iron;

Fig. 2 is a view in longitudinal section of the iron shown in Fig. 1 showing a form of heating element which is integrally united with the iron; and

Fig. 3 is a transverse sectional view showing the manner in which the heating element is made to be removably mounted in the iron.

Fig. 4 is a view similar to Fig. 2 showing the integral construction of the liner and preformed heating element.

One of the principal features of the present invention is the use of a refractory material for making the heating element of the iron by which the heat developed in the resistance Wire used for heating will be transferred by a substantially perfect or 100% eiliciency from the Wire to the iron being heated. This refractory material has been invented by me and is commonly known on the market by the tradename Semhet Semhet is made up of a mixture by weight of substantially 60 parts ferrosilicon, 40 parts fine Zircon and 6 parts HJPO4 (phosphoric acid). The ferrosilicon preferably contains '75% or higher of metallic silicon, the rest being iron. When Semhet is heat treated and fused at temperatures as low as 50o-600 F. its dielectric properties are good but the dielectric properties of Semhet increase very rapidly as the firing temperature of the material is increased. For example. the dielectric properties of Semhet are two or three times as good when the material has been fused at 1800 as when the material is fused at 500 F. Accordingly in preparing a heating element to pass the usual underwriters g554 specifications it is desirable to use a Semhet body which is heat treated at tempera-tures of 1800 F. or higher. With this high temperature treated Semhet the dielectric properties are suinciently good to stand a very high wattage and this product at the same time has a thermal conductivity better than steels. Due to the high dielectric property of Semhet the electrical resistance Wire is preferably embedded Within the body of the Semhet and the heat transfer takes place directly from the Wire to the metal of the iron by conduction of the Semhet from the resistance Wire to the iron.

Most irons for both domestic and industrial purposes are made from cast iron and these castings have irregularities therein. Accordingly when heating elements are composed of preformed elements made of resistance wires within an envelope often there is only a point to point contact between the envelope and the body of the iron. This condition clearly interferes with the heat transfer from the heating element to the iron.

Semhet has the admirable property of being capable of being united integrally or Welded to the' iron and therefore the heat transfer loss in passing from the Semhet to the iron is substantially zero.

To make domestic irons in accordance'with the present invention it is 4desirable that the Semhet heating element shall be integrally united With the iron because such heating element lasts indefinitely and does not need to be replaced. For industrialirons which are subjected continuously to high temperatures, it is often desirable to have the heating element removably mounted so that it can be replaced in case of the failure of the resistance heating Wire.

To make an iron having a heating element integrally united therein the iron body I0 which is made of a casting is provided with a cavity I2 (Fig. 2) in which is mounted a heating element I4. The heating element I4 preferably is a prf` formed and preflred element which is heated in a neighborhood of 1800 F. in order to provide a high dielectric property. The preformed element is preferably made by molding the element in a mold having a shape simulating the shape of the cavity of the iron but slightly smaller than the cavity. The ingredients of Semhet used in making the element are preferably used in the dry form, the Semhet being distributed around a resistance heating wire I6 which is placed within the body of the heating element. The Semhet with the resistance Wire therein is subjected to a molding pressure so that it can be handled to be fired. When it is red it is fused into an integral metallic body that can be readily handled. The ends of the resistance wire IS are preferably secured to terminals I8 composed of stainless steel material or the like which are capable of withstanding high temperatures and which are pcsitioned at the point where the electrical connections are made. The terminals I8 are preferably embedded in the Semhet material so that the I Semhet material rigidly supports the terminals so that they will not be broken orf while the electrical connectors are being attached thereto and while the iron is being assembled. The resistance wire I6 is preferably a high temperature alloy such as those alloys now commonly known on the market as Nichrome and Kanthol- These materials become quite britle when they are rapidly heated and cooled and therefore it is very desirable that they should be embedded aiaoos and supported within the body of a refractory heating element. Some of these types of heating Wires furthermore break. under the repeated heating and cooling to the point where they are very poor electrical conductors. It has been found therefore that if the resistance heating wire is made up of a stranded wire, that is a plurality of fine wires which will give the necessary resistance heating capacity, that such ne stranded wires will overcome the objection of the fracture of the wire to the point where it will always be a conductor.

The pressed, preformed heating element is preferably heat cured at temperatures from 1600 to 2000 F., this curing being accomplished on the element alone. The heat curing of the element cannot be effected While the element is in the iron because such high temperatures tend to warp and destroy the iron. Furthermore these irons are often plated with material such as nickel and chromium and the high temperature treatment tends .to injure the plating.

In order to unite the heating element integrally with the iron a preformed heating element I4 is forced under pressure into the cavity in the iron after the bottom and each wall of the cavity have been coated with a lining of liquid slurry of Semhet. This slurry fills the entire gap between the edge and bottom of the heating element and the edges and bottom of the cavity in the heating iron, After the element has been pressed into position in the iron the entire assembled body is then heat cured in a furnace to a temperature of approximately 1000D to 1200 F. This temperature is continued from thirty minutes to two hours or for a time sufficient to fuse the slurry composition and permanently unite the heating element'with the walls of the iron.

All irregularities in the surface of the cavity of the iron and any irregularities in the surface of the heating element are filled with the liquid slurry material at the time that the element is pressed into position and therefore when the body is united by heat there is an integral, intimate contact between the heating element and the iron. This contact therefore permits practically a perfect heat transfer from the heating element to the iron and permits this transfer to take place over the entire surface of the heating element.

If it is desired to have the heating element removable, substantially the same process is employed as that described above with the exception that the heating element I4 (Fig. 3) is inclosed in a thin paper Wrapper (not shown) at the time that it is pressed into position in thecavity in the iron. This paper stays in position at the time the iron is fired, but the firing of the iron tends to char and carbonize the paper to the point that it completely disintegrates. After the firing has been completed the element may be removed by working a sharp instrument around in the crack where the paper has been charred. The charred paper is removed and the element replaced. Since the paper conforms to the shape of the element and the lining'ZI formed by the slurry there will be .an intimate, direct contact between the heating element and the iron by which an ecient heat transfer may be effected.

Another method of making an iron by which the heating element is integrally united with the iron may be described as follows:

The cavity I 2 of the iron is coated with a` percent of 85% HsPOl. The lining is dried and baked. After the lining has been cured by heat the same type of resistance wire is positioned within the cavity and Semhet preferably in a moist wet form is poured into the cavity around the resistance wire and the entire body is then fired at a temperature of 1000 to 1200o F. At this temperature of firing the dielectric properties of the Semhet are not quite as high as if the `Semhet had been cured at a temperature of 1600 to 2000* and therefore the high dielectric properties of the zircon are depended upon to definitely insulate the inside surface of the cavity of the iron. When the Semhet is heat treated inside of the lining there is an intimate bond between the Semhet and the Zircon lining whereby the heating element is integrally united with the iron proper. 'I'his bonded zircon on the Semhet has a very high thermal conductivity and therefore gives a very efficient heat transfer.

By this method it will be apparent that the zircon lining will conform to the irregularities of the surface of the cavity of the iron and since' the Semhet is intimately united with the Zircon lining an efficient heat transferring element is provided.

It will be understood that the composition of Semhet may be modified within reasonable limits and the temperatures of curing these materials .may be modified within the skill of the chemist.

The iron of the type illustrated in the drawing is preferably for industrial purposes and is provided with a steam duct by which steam may be continuously supplied to the work while the pressing and 'ironing operation continues. This is accomplished by means of a duct 20 which extends around the entire periphery of the iron.v

From the duct 20 a series of small outlets 22 pass to the lower surface of the iron. A steam inlet connection 24 is provided that is normally \connected with a flexible steam hose 26 by which steam is admitted to the duct, preferably the hose should be provided with a valve by whichv the admission of steam may be controlled. 'Ihe steam entering the duct 20 will be at substantially atmospheric pressure and a saturated steam. However, the temperature of the wire is higher than the temperature of the saturated steam so that as the steam passes through the duct the steam will be superheated. The requirement of the iron to superheat the steam requires a large amount of heat and the heating element of the present invention is designed to take care of this additional heat. The heat from the steam also helps to press the fabrics as well as the heat of theA iron.

Ihe preferred form of the invention having been thus described what is claimed as new is:

1. A method of making an electrically heated iron comprising forming an iron body with a cavity to receive a heating element, forming a heating plate of ashape simulating and slightly smaller than the 'said cavity by molding under pressure a`composition having a high dielectric strength and a thermal heating conductivity greater than that of steel with an electrical resistance wire embedded within the plate, firing the plate at a temperature approximately 1600 to 1800"4 F. to consolidate the plate, coating the cavity of the iron with a water slurry of said refractory composition, enclosing the faces of the plate which enter the cavity within a thin flexible paper and pressing the enclosed plate within the cavity so that the slurry will fill the space between the paper and the inner wall of the iron cavity, firing the iron with the 'element in place to fuse the slurry and char the paper, removing the paper char after firing and replacing the heating element, providing electrical connections with the resistance heating wire, and securing a cover and handle to the iron over the heating element.

2. The method defined in claim 1 wherein the composition used for making the heating plate is a heat-hardenable composition comprising by weight 60 parts of ferrosilicon, 40 parts of zircon and 6 parts of phosphoric acid (HaPOl).

3. An electric iron comprising an iron body having a cavity therein, a firing-cured heat conductant refractory liner united `to the iron surface of the cavity; a preformedand heat-` red heating element composed of a heathardened refractory comprisingl by weight 60 parts ferrosilicon, 4Q parts zircon, 6 parts H3PO4 removably mounted within the lined cavity making full surface contact with the liner and having an electrical resistance wire embedded therein, said refractory heating element having a high dielectric property and having a thermal conductivity equal to steel.

4. An electric iron comprising an iron body having a cavity therein, a ring-cured liner on the surface of the cavity comprising a refractory composition of approximately 94 to 90% fine mesh zircon and 6 to 10% H aPOl, a preformedy refractory heating element which is heat-cured at a temperature of'16002000 F. removably ductant refractory liner united to the iron surface of the cavity, a preformed and heat-fired heating element composed of a heat hardened refractory having 'an electrical resistance wire embedded therein, said refractory heating element having a high dielectric property and having a high thermal conductivity, said element being removably mounted within said lined cavity and making a full surface contact with the liner.

JOHN D. MORGAN. 

